In the early 2000s, Swedish scientists and the fishing industry introduced and adapted the Norwegian Nordmøre shrimp grid for Norway lobster trawl fishing – the Swedish grid. The aim was to minimise by-catches of demersal roundfish like cod, without losing Norway lobster.
In 2004 the grid became mandatory in Swedish waters, which made it possible to continue trawling Norway lobster despite weak cod stocks.
Norway lobster trawl fishing is also characterised by a high discard ratio of undersized lobster. To meet the upcoming landing obligation and limitation of quotas for by-catch species, fishers wanted to develop the grid further. Swedish fishermen Bertil Andersson (VG-350 Althea) and Ingvar Olsson (SD-669 Palermo) contacted the Swedish Secretariat for Selective Fishing to present new ideas. In 2015, development was completed and the trawl was evaluated scientifically. It was found to be highly effective in further reducing by-catches in grid trawl fishery.
1. Traditional trawl. Non specie selective, high discard rates.
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2. Swedish grid trawl. Large fish are deflected out by the grid, smaller fish and Norway lobster pass through the grid and enter the codend.
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3. The Palermo grid trawl. Dual grid system – releases undersized Norway lobsters from catch through the lower tighter gridpanel beneath the trawl.
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4. Althea Grid Trawl. Increased selectivity by mesh in the codend – removing smaller individuals of both cod (square mesh panel) and flatfish (diamond mesh panel).
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Scientific comparison of catches between the Swedish grid trawl and the Althea grid trawl, targeting Norway lobster. All other species and undersized Norway lobster is counted as unwanted by-catch.
|
Species |
Swedish grid |
Althea grid |
Difference |
|
Norway lobster |
20,2 | 17,8 | -12 % |
|
Norway lobster |
8,3 | 3,3 | - 60 % |
|
Whiting |
5,3 | 1,2 | - 77 % |
| Cod | 5,2 | 1,3 | - 75 % |
| Plaice | 21,7 | 8,3 | - 62 % |
| Dab | 60,1 | 8,1 | - 86 % |
| Long rough dab | 17,8 | 2,5 | - 86 % |
Hans C. Nilsson, Researcher
Department of Aquatic Resources, Institute of Marine Research, SLU hans.nilsson@slu.se , +46 10 478 40 40
Daniel Valentinsson, Researcher
Department of Aquatic Resources, Institute of Marine Research, SLU daniel.valentinsson@slu.se, +46 10 478 40 49